Low-voltage circuit breaker

ABSTRACT

A low-voltage circuit breaker, comprising:
     at least one first fixed contact, which is electrically connected to a terminal for connection to an electric circuit;   a rotating moving contact, which comprises a central body from which at least one first arm protrudes, an active surface being provided at the end of the first arm, the active surface being associable/separable with respect to the fixed contact by means of a rotation of the moving contact;   a rotating contact supporting shaft, which is functionally connected to an actuation mechanism of the circuit breaker and is provided with a seat that accommodates the central body of the moving contact so that the first arm protrudes externally from the seat, at least one first spring being furthermore arranged in the contact supporting shaft and being functionally coupled to the moving contact and suitable to ensure, when the circuit breaker is closed, an adequate contact pressure between the active surface and the first fixed contact; its particularity consists of the fact that at least one first abutment surface is provided on the central body of the moving contact and is suitable to act, during a rotation of the moving contact caused by a short-circuit, against a complementarily shaped surface formed in the seat of the shaft, so that at least part of the energy accumulated by the rotating moving contact during its rotation is transmitted directly to the shaft.

The present invention relates to a low-voltage circuit breaker, i.e.,for applications with operating voltages up to 1000 volts.

BACKGROUND OF THE INVENTION

Low-voltage industrial electrical systems characterized by high currentsand power levels normally use specific devices, commonly known in theart as automatic power circuit breakers.

These circuit breakers are designed so as to provide a series offeatures required to ensure the correct operation of the electricalsystem in which they are inserted and of the loads connected to it. Forexample, they ensure the nominal current required for the various users,allow correct insertion and disconnection of the loads with respect tothe circuit, protect the loads against abnormal events such asoverloading and short-circuits by opening the circuit automatically, andallow to disconnect the protected circuit by galvanic separation or byopening suitable contacts in order to achieve full isolation of the loadwith respect to the electric power source.

Currently, these circuit breakers are available according to variousindustrial embodiments, the most common of which entrusts the opening ofthe contacts to complicated kinematic mechanisms that utilize themechanical energy stored beforehand in special opening springs and aregenerally triggered, in case of electrical fault, by an appropriateprotection device, typically a relay.

In certain operating conditions, particularly when the presumedshort-circuit current can assume significantly high values, the use ofdevices that utilize in a traditional manner the energy that can beaccumulated in the opening springs can be scarcely efficient anduneconomical for opening the contacts; in such cases, one normallyresorts to special types of automatic circuit breaker that havetechnical solutions aimed at increasing their breaking capacity.

Among the technical solutions that are currently most widely used, thereare two that are often used in combination. In particular, a firstsolution forces the current to follow a given path, so that when a shortcircuit occurs, electrodynamic repulsion forces occur between thecontacts. These repulsion forces generate a useful thrust that helps toincrease the separation speed of the moving contacts with respect to thefixed contacts; in this manner, the intervention time is reduced and thepresumed short-circuit current is prevented from reaching its maximumvalue.

The second solution doubles the fixed contacts and the moving contacts.In this case, the flow of current is interrupted in each pole of thecircuit breaker in two separate regions that are arranged electricallyin series to each other, so that each region is subjected to a lowermechanical and thermal stress.

A particularly critical aspect of known types of circuit breaker is thefact that the presence of electrodynamic repulsion forces, whilecontributing positively to the generation of the thrust useful forcontact separation on the one hand, on the other hand helps the movingcontact structure to reach the end of its stroke at high speed andtherefore with great energy. This generally tends to cause violentimpacts against the case of the circuit breaker, with the possibility ofdamaging it, and can therefore require the use of additional cushioningelements; moreover, bouncing of the moving contacts toward the fixedcontacts and undesirable restrikes of the electric arc can occur. In thecase of circuit breakers with double contacts, the likelihood ofbouncing and restriking of the electric arc can be increased by thepresence of additional springs, which are usually associated with thestructure of each moving contact in order to facilitate an evendistribution of the mechanical pressure on the two surfaces for couplingbetween each moving contact and the corresponding fixed contacts.

BRIEF SUMMARY OF THE INVENTION

The aim of the present invention is to provide a low-voltage circuitbreaker that allows to obviate the drawbacks noted above and inparticular in which opening in the short-circuit condition occurs in amanner that is optimized and functionally more effective than in knownsolutions, at the same time eliminating or at least minimizing theimpacts that the moving contact can have against the case of the circuitbreaker and the consequent negative effects caused by said impacts.

This aim and other objects that will become more clear hereinafter areachieved by a low-voltage circuit breaker, comprising:

at least one first fixed contact, which is electrically connected to aterminal for connection to an electric circuit;

a rotating moving contact, which comprises a central body from which atleast one first arm protrudes, an active surface being provided at theend of said first arm, said active surface being associable/separablewith respect to said fixed contact by means of a rotation of said movingcontact;

a rotating contact supporting shaft, which is functionally connected toan actuation mechanism of the circuit breaker and is provided with aseat that accommodates the central body of the moving contact so thatthe first arm protrudes externally from said seat, at least one firstspring being furthermore arranged in said contact supporting shaft, saidfirst spring being functionally coupled to the moving contact and beingsuitable to ensure, when the circuit breaker is closed, an adequatecontact pressure between the active surface and the first fixed contact;characterized in that at least one first abutment surface is provided onsaid central body of the moving contact and is suitable to act, during arotation of the moving contact caused by a short-circuit, against acomplementarily shaped surface formed in said seat of the shaft, so thatat least part of the energy accumulated by the rotating moving contactduring its rotation is transmitted directly to the shaft.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Further characteristics and advantages of the invention will becomebetter apparent from the description of preferred but not exclusiveembodiments of the circuit breaker according to the invention,illustrated only by way of non-limitative example in the accompanyingdrawings, wherein:

FIG. 1 is a plan view of a first embodiment of the assembly constitutedby the contact supporting shaft, the moving contact with a single arm,and a fixed contact, which can be used in the circuit breaker accordingto the invention;

FIG. 2 is a plan view of a second embodiment of the assembly constitutedby the contact supporting shaft, the moving contact with a single arm,and a fixed contact, which can be used in the circuit breaker accordingto the invention;

FIG. 3 is a plan view of a third embodiment of the assembly constitutedby the contact supporting shaft, the moving contact with a single arm,and a fixed contact, which can be used in the circuit breaker accordingto the invention;

FIG. 4 is a plan view of the moving contact of FIG. 1 during abutmentagainst the contact supporting shaft, during the separation of theactive surface from the respective fixed contact following a shortcircuit;

FIG. 5 is a partial perspective view of a contact supporting shaftcoupled to a moving contact and to a mechanism for the actuation of thecircuit breaker;

FIG. 6 is a plan view of a possible embodiment of the assemblyconstituted by the moving contact and the contact supporting shaft, fora circuit breaker with double contacts.

DETAILED DESCRITION OF THE INVENTION

In the following description, for the sake of greater simplicity indescription, reference is made to a single pole of the circuit breaker,without thereby intending to limit in any way the scope of theinvention, since the conceived solution can be applied to all the polesof a low-voltage circuit breaker having any number of poles. Moreover,in the various figures identical reference numerals designate identicalor technically equivalent elements.

With reference to the cited figures, a pole of the low-voltage circuitbreaker according to the invention generally comprises at least onefirst fixed contact 1, which is connected electrically, by means of anappropriately configured conductor 2, to a terminal for connection to anelectric circuit, according to embodiments that are widely known in theart and are therefore not described in detail; the pole furthermorecomprises a rotating moving contact 10 and a rotating contact supportingshaft 20, which is shown in cross-section in FIGS. 1 to 4 for the sakeof greater clarity of illustration and is functionally connected to themoving contact 10 and to a circuit breaker actuation mechanism 30. Asshown in detail in FIG. 5, said actuation mechanism 30 generallycomprises a kinematic system with opening springs 31 and allows toconnect functionally the contact supporting shaft 20 to a lever for themanual actuation of the circuit breaker 32. The circuit breaker,moreover, is usually provided with a protection device (not shown) forprotection against electrical faults, typically a relay, which tripswhen an electrical fault occurs, causing the actuation of the actuationmechanism 30, with consequent rotation of the contact supporting shaft20 and release of the circuit breaker. The operation of the protectionrelay and of the actuation mechanism 30, as well as the correspondingmethods for their functional connection to each other and to the otherparts of the circuit breaker, are also widely known in the art andtherefore are not described further.

As shown in detail in FIGS. 1 to 4, the rotating contact supportingshaft 20 has a seat 21 that is contoured appropriately so as to have atleast one interaction surface 22, and a pivot 23 is fixed in the seat21.

In turn, the rotating moving contact 10 has a contoured central body 11,from which at least one first arm 12 protrudes; an active surface 13,for example a contact plate or pad, is arranged at the end of said armand can be coupled/separated electrically with respect to the fixedcontact 1 following the rotation of said moving contact 10. Inparticular, in the illustrated embodiments, the moving contact 10 isfunctionally connected to the shaft 20 and is arranged so that thecentral part 11 is accommodated in the seat 21, so that the end of thearm 12 protrudes transversely outside it; preferably, the moving contact10 is connected to the shaft 20 by coupling a hole 14 formed in thecentral body 11 to the pivot 23, according to a solution that isadvantageous from the point of view of manufacture and assembly.Clearly, the functional connection between the shaft 20 and the movingcontact 10 might be provided in different manners, for example byproviding the pivot on the body of the moving contact and the couplinghole in the shaft, or by providing a floating coupling exclusively bymeans of one or more springs arranged in the seat 21 and suitablyconnected to the shaft and to said moving contact, or in other manners,provided that they are compatible with the application.

Advantageously, in the circuit breaker according to the invention, onthe contoured central body 11 of the moving contact 10 there is at leastone first abutment surface 15, which is suitable to interactfunctionally against the complementarily shaped surface 22 for thepurposes that will become better apparent in detail hereinafter.

Preferably, in the embodiments shown in FIGS. 1 and 2, at least onefirst cam-like surface 16 is furthermore provided on the central body 11of the moving contact 10 and is contiguous to the abutment surface 15and arranged between said abutment surface and the extension of the arm12; furthermore, at least engagement means 24 and an additional pivot 25are arranged on the shaft 20 on mutually opposite sides with respect tothe body of the moving contact 10. In particular, in the embodimentshown in FIGS. 1 and 4, the engagement means 24 preferably comprise asecond pivot 24, which is rigidly fixed to the shaft 20, while the thirdpivot 25 is functionally coupled to the moving contact 10 so that it canmove with respect to it and is arranged so that its ends are inserted inslots 26 formed in the contact supporting shaft 20.

The embodiment shown in FIG. 2, instead, uses additional engagementmeans, which preferably comprise a fourth pivot 27 which, taking asreference the first pivot 23, is fixed to the shaft 20 in asubstantially symmetrical position with respect to the second pivot 24;in turn, the third pivot 25 is functionally coupled to the movingcontact 10 so that it can move with respect to it and is connected tothe fourth pivot 27 by virtue of two linkages 28 (only one of which isshown in FIG. 2), which are arranged in the seat 21 of the shaft 20along two opposite sides of the moving contact 10 which aresubstantially parallel to each other.

At least one spring is generally associated with the moving contact 10and is suitable to ensure, when the circuit breaker is closed, anadequate contact pressure between the active surface 13 and thecorresponding fixed contact 1. In particular, the circuit breakeraccording to the invention preferably uses at least two traction springs8 (only one of which is visible in FIGS. 1 to 4), each anchored to thesecond pivot 24 and to the third pivot 25 and arranged on mutuallyopposite sides with respect to the arm 12 of the moving contact 10.

The operation of the circuit breaker according to the invention is nowdescribed with reference, by way of example, to the embodiment shown inFIGS. 1 and 4.

In operating conditions, when a short circuit occurs, the electrodynamicrepulsion forces generated in the electrical parts crossed by thecurrent trigger the rotation of the moving contact 10, which startingfrom the position shown in FIG. 1 moves toward the position shown inFIG. 4, in which the abutment surface 15 abuts against the correspondingsurface 22; in this situation, owing to the interaction between thesurfaces 15 and 22, there is the great advantage that at least part ofthe kinetic energy possessed by the moving contact 10 during therotation is transmitted directly to the contact supporting shaft 20 andtherefore also distributed among the mechanical parts that are connectedthereto. In a manner that is extremely advantageous and entirelyinnovative with respect to the known art, the energy transmitted by themoving contact 10 to the shaft 20 is therefore not only removed from thepossible impact against the case of the circuit breaker but is actuallyused to overcome the inertia of said shaft and trigger its rotationprior to the tripping of the protection relay, which in any case actsimmediately after the above described effect and causes the release ofthe actuation mechanism 30 in a fully conventional manner. Therefore,this allows, with respect to known solutions, to perform more rapidopening actions and to reduce the mechanical and electrical stressesthat the active parts must withstand in short-circuit conditions, withthe beneficial consequence that the behavior of the circuit breaker overits useful life is improved significantly and its useful life is itselfextended.

Furthermore, the fact that the energy accumulated by the moving contactduring its rotation is utilized to obtain the effect described aboveprevents all the accumulated kinetic energy from discharging directlyonto the case of the circuit breaker, reducing every cause of possiblebouncing of the moving contact 10 and therefore of restriking of theelectric arc. This positive effect can be increased if the constructiveconfigurations shown in FIGS. 1 and 2 are used. In these cases, thepivot 25, under the action of the corresponding springs associatedtherewith and of the linkages 28 in the embodiment of FIG. 2, is in factarranged in abutment against the wall of the cam-like surface 16; thisinteraction facilitates the generation of a force, indicated by thearrow A, that ultimately produces a moment that tends to keep the activesurface 13 of the moving contact 10 coupled to the fixed contact. Duringopening caused by a short circuit, the rotation of the moving contact 10entails the sliding of the pivot 25, which under the action of thesprings 8 interacts with the cam-like surface 16, remaining in directcontact with it, with relative sliding of the parts in contact; thisleads to a variation in the direction of the force A, with a gradualreduction of its lever arm 29 until, as shown in detail in FIG. 4, theinteraction between the pivot and the cam-like surface is such as toplace the line of action the forces A under center with respect to thepivot 23 and therefore one has a lever arm 29 whose sign is opposite tothe initial phase. In this situation, therefore, there is a mechanicalmoment that matches the direction of rotation of the moving contact 10that helps to keep the moving contact 10 in the position it has reached,contrasting any bouncing and making it substantially unnecessary to useadditional latching systems.

In any case, it should be noted that the innovative result of thetransmission of energy from the moving contact to the rotating shaftrequires only the contour of the moving contact to be provided with theabutment surface required to interact with the corresponding surfaceformed on the shaft and is substantially independent of the type offunctional coupling between the shaft and the moving contact and of thecontour of the remaining part of said moving contact; for example, inaddition to the solutions described above, it would be possible to use amoving contact that is contoured without cam-like surfaces, as shownschematically in FIG. 3, or to connect the moving contact to the shaftby using one or more coupling springs conveniently arranged in the seatwithout using pivots, or in any other manner so long as it is compatiblewith the application.

The solutions described above for a single-contact circuit breaker canbe implemented easily and just as advantageously in the case of circuitbreakers with double contacts; in this case it is in fact substantiallysufficient to duplicate, symmetrically with respect to the rotationaxis, the shape and the functional parts of the invention.

An example in this regard is shown schematically in FIG. 6. As shown insaid figure, the circuit breaker is provided with a first fixed contact1 and with a second fixed contact 3, which are connected electrically,by virtue of appropriately configured conductors 2, to correspondingterminals for connection to an electric circuit. In turn, the rotatingmoving contact 10 has a contoured central body 11 from which two arms 12protrude; two active surfaces 13 are arranged at the ends of said armsand in mutually opposite directions with respect to the rotation axisand can be coupled/separated with respect to the corresponding fixedcontacts 1 and 3 as a consequence of the rotation of said moving contact10. Advantageously, in this embodiment, on the contoured central body 11of the moving contact 10 there are first and second abutment surfaces 15on mutually opposite sides and substantially symmetrically with respectto the rotation axis and therefore with respect to the bole 14;correspondingly, the seat 21 of the shaft 20 is contoured so as to formtwo interaction surfaces 22, against each of which an abutment surface15 acts in a manner that is functionally entirely similar to what hasbeen described for a moving contact with a single arm.

Clearly, even in the case of a circuit breaker with double contacts itis possible to provide the functional connection between the shaft andthe moving contact according to various constructive configurations andto adopt or not also the contour with the cam-like surfaces.

For example in the embodiment shown in FIG. 6, on the central body ofthe moving contact 10 there are two contiguously arranged cam-likesurfaces 16, each having a corresponding abutment surface 15;correspondingly, with respect to the solution with single contacts, onthe shaft 20 there are also two additional pivots: with reference to thepivot 23, a fourth pivot 34 is fixed to the shaft in a substantiallysymmetrical position with respect to the second pivot 24, and a fifthpivot 35 is arranged symmetrically with respect to the third pivot 25and is functionally equivalent thereto. Two additional springs 8 areanchored to the two pivots 34 and 35 and are also arranged on mutuallyopposite sides with respect to the second arm 12.

Similar modifications can be adopted in passing from a single-contactcircuit breaker to a double-contact circuit breaker for the embodimentsshown in FIGS. 2 and 3. For example, in the case of FIG. 2 it issufficient to use a fifth pivot which is arranged, relative to the pivot23, substantially symmetrically with respect to the pivot 25 and isfunctionally equivalent thereto; in this case, said fifth pivot 25 canbe connected to the second pivot 24 by virtue of an additional pair oflinkages 28, and it is possible to use two additional springs 8 that areanchored to the pivot 27 and to said fifth pivot.

It should be noted that in the various embodiments, both with thesingle-arm moving contact and with the double-arm moving contact, thefixed pivots 24 or 27 or 34 can be replaced in a fully equivalent mannerby other engagement means that allow the engagement of the ends of thesprings 8 in a manner that is functionally similar to the action of asingle fixed pivot: for example, it is possible to use two pivots thatare structurally independent of each other and are fixed to the shaft,or two coupling elements coupled to the shaft, or two seats formedtherein and suitable to allow the anchoring of the ends of the springs8, or other means, so long as they are compatible with the application.

In practice it has been found that the circuit breaker according to theinvention fully achieves the intended aim, providing a significantseries of advantages with respect to the known art and being usable bothas a standard circuit breaker and as a current limiter.

The circuit breaker thus conceived is susceptible of numerousmodifications and variations, all of which are within the scope of theinventive concept; all the details may furthermore be replaced withother technically equivalent elements. In practice, the materialsemployed, as well as the dimensions, may be any according to therequirements and the state of the art.

1. A low-voltage circuit breaker, comprising: at least one first fixedcontact, which is electrically connected to a terminal for connection toan electric circuit; a rotating moving contact, which comprises acentral body from which at least one first arm protrudes, an activesurface being provided at the end of said first arm, said active surfacebeing associable/separable with respect to said fixed contact by meansof a rotation of said moving contact; a rotating contact supportingshaft, which is functionally connected to an actuation mechanism of thecircuit breaker and is provided with a seat that accommodates thecentral body of the moving contact so that the first arm protrudesexternally from said seat, at least one first spring being furthermorearranged in said contact supporting shaft, said first spring beingfunctionally coupled to the moving contact and being suitable to ensure,when the circuit breaker is closed, an adequate contact pressure betweenthe active surface and the first fixed contact; characterized in that atleast one first abutment surface is provided on said central body of themoving contact and is suitable to act, during a rotation of the movingcontact caused by a short-circuit, against a complementarily shapedsurface formed in said seat of the shaft, so that at least part of theenergy accumulated by the rotating moving contact during its rotation istransmitted directly to the shaft.
 2. The circuit breaker according toclaim 1, characterized in that said first abutment surface formed on thecentral body of the moving contact acts against said complementarilyshaped surface so as to trigger, in the short-circuit condition, therotation of the contact supporting shaft before the intervention of saidactuation mechanism.
 3. The circuit breaker according to claim 2,characterized in that a first pivot is fixed to said contact supportingshaft and is coupled with play in a hole formed in said central body ofthe moving contact, at least one first cam-like surface beingfurthermore formed on said central body and being arranged contiguouslyto said first abutment surface.
 4. The circuit breaker according toclaim 1, characterized in that a first pivot is fixed to said contactsupporting shaft and is coupled with play in a hole formed in saidcentral body of the moving contact, at least one first cam-like surfacebeing furthermore formed on said central body and being arrangedcontiguously to said first abutment surface.
 5. The circuit breakeraccording to claim 1, characterized in that it comprises at least onesecond pivot, which is fixed to the shaft, and a third pivot, which isfunctionally coupled to the moving contact and can slide in slots formedin said shaft, said second and third pivots being arranged on mutuallyopposite sides with respect to the body of the moving contact, a firstspring and a second spring being furthermore anchored to the second andthird pivots and being arranged along two opposite sides of the arm ofthe moving contact, said third pivot interacting functionally with saidfirst cam-like surface so as to generate a mechanical moment thatmatches the direction of rotation of the moving contact dining at leastone final portion of the separation of the active surface from the fixedcontact in a short-circuit condition.
 6. A The circuit breaker accordingto claim 5, characterized in that a second cam-like surface isfurthermore formed on said central body and is contiguous to said secondabutment surface, and in that with reference to said first pivot on saidshaft there is also a fourth pivot, which is fixed to the shaft in asubstantially symmetrical position with respect to the second pivot, andthere is a fifth pivot, which is arranged substantially symmetrically tothe third pivot and is coupled functionally to the moving contact andable to slide in slots formed in said shaft, a third spring and a fourthspring being anchored to the fourth end fifth pivots and being arrangedalong two opposite sides of the moving contact, the fifth pivotinteracting functionally with the second cam-like profile so as togenerate a mechanical moment that matches the direction of rotation ofthe moving contact during at least one final portion of the step ofseparation of the active surfaces from the corresponding fixed contactsin a short-circuit condition.
 7. The circuit breaker according to claim1, characterized in that it comprises at least one second pivot and onethird pivot, which are fixed to the shaft in a substantially mutuallysymmetrical position with respect to said first pivot, and a fourthpivot, which is functionally coupled to the moving contact so that itcan move with respect to it, said third and fourth pivots being mutuallyconnected by virtue of a first linkage and a second linkage, which arearranged in said seat of the shaft along two opposite sides of themoving contact, a first spring and a second spring being furthermoreanchored to the second and fourth pivots and being arranged along twoopposite sides of the rotating moving contact, said fourth pivotinteracting functionally with said first cam-like surface so as togenerate a mechanical moment that matches the direction of rotation ofthe moving contact during at least one final portion of the separationof the active surface from the fixed contact in a short-circuitcondition.
 8. The circuit breaker according to claim 7, characterized inthat a second cam-like surface is furthermore formed on said centralbody and is contiguous to said second abutment surface, and in that itcomprises a fifth pivot that is functionally coupled to the movingcontact so that it can move with respect to it, said fifth pivot beingconnected to the second pivot by means of a third linkage and a fourthlinkage arranged in said seat of the shaft along two opposite sides ofthe moving contact, a third spring and a fourth spring being anchored tothe fifth and fourth pivots and being arranged along two opposite sidesof the moving contact, said fifth pivot interacting functionally withsaid second cam-like surface so as to generate a mechanical moment thatmatches the direction of rotation of the moving contact during at leastone final portion of the separation of the active surfaces from thefixed contacts in a shaft-circuit condition.
 9. The circuit breakeraccording to claim 13, characterized in that it comprises two fixedcontacts that are connected electrically to corresponding terminals forconnection to an electric circuit, and in that said rotating movingcontact comprises a central body from which a first arm and a second armprotrude, two active surfaces being provided at the ends of said armsand on mutually opposite sides with respect to the rotation axis, saidsurfaces being associable/separable with respect to said fixed contactsby virtue of the rotation of said moving contact, at least one firstabutment surface and one second abutment surface being formed on saidcentral body and being arranged on mutually opposite sides with respectto said rotation axis, said surfaces being suitable to act, during arotation of the moving contact caused by a short-circuit, against twocomplementarily shaped surfaces formed in said seat of the shaft. 10.The circuit breaker according to claim 9, characterized in that saidfirst and second abutment surfaces are arranged on the central body ofthe moving contact and are substantially symmetrical with respect tosaid rotation axis.
 11. The circuit breaker according to claim 9,characterized in that a second cam-like surface is furthermore formed onsaid central body and is contiguous to said second abutment surface, andin that with reference to said first pivot on said shaft there is also afourth pivot, which is fixed to the shaft in a substantially symmetricalposition with respect to the second pivot, and there is a fifth pivot,which is arranged substantially symmetrically to the third pivot and iscoupled functionally to the moving contact and able to slide in slotsformed in said shaft, a third spring and a fourth spring being anchoredto the fourth and fifth pivots and being arranged along two oppositesides of the moving contact, the fifth pivot interacting functionallywith the second cam-like profile so as to generate a mechanical momentthat matches the direction of rotation of the moving contact during atleast one final portion of the step of separation of the active surfacesfrom the corresponding fixed contacts in a short-circuit condition. 12.The circuit breaker according to claim 9, characterized in that a secondcam-like surface is furthermore formed on said central body and iscontiguous to said second abutment surface, and in that it comprises afifth pivot that is functionally coupled to the moving contact so thatit can move with respect to it, said fifth pivot being connected to thesecond pivot by means of a third linkage and a fourth linkage arrangedin said seat of the shaft along two opposite sides of the movingcontact, a third spring and a fourth spring being anchored to the fifthand fourth pivots and being arranged along two opposite sides of themoving contact, said fifth pivot interacting functionally with saidsecond cam-like surface so as to generate a mechanical moment thatmatches the direction of rotation of the moving contact during at leastone final portion of the separation of the active surfaces from thefixed contacts in a short-circuit condition.